Learning German, and every week I run into a word that English just doesn't have. "Doch" is the obvious one. It's this tiny word that means "yes actually, contrary to what you just said", and English needs a whole sentence for it.
"Gemütlich" is the other one that got me. Everyone translates it as "cozy" but it's not just cozy. It's the whole vibe of being warm and relaxed and among people you like. Cozy is a couch and a blanket. gemütlich is a three hour dinner with friends.
What else is out there? French, Italian, Dutch, Polish, whatever. Which word in your language makes English feel kind of basic when you stop to think about it?